200 research outputs found
No "big trips" for the universe
It has been claimed in several papers that a phantom energy-dominated
universe can undergo a ``big trip'', i.e., tunneling through a wormhole that
grows faster than the cosmic substratum due to the accretion of phantom energy,
and will reappear on the other mouth of the wormhole. We show that such claims
are unfounded and contradict the Einstein equations.Comment: 8 pages, latex, to appear in Phys. Lett.
Inferring the occurrence of regime shifts in a shallow lake during the last 250 years based on multiple indicators
Regime shifts are ecosystem-scale phenomena. In lake studies, most supporting evidence is frequently based on a single state variable. We examined the sediment record of the shallow lake Blanca Chica (Argentina) to explore the response of multiple proxies belonging to different trophic levels (nutrients, chlorophyll and carotenoid pigments, diatoms, Cladocera remains, and Rotifera resting eggs) over the last 250 yr. We explored different ecological indicators to assess changes consistent with regime shifts. To do so, first we identified the timing of transitional periods on multiple-proxies. Then, we explored (1) the nature of the change (linear versus non-linear dynamics), (2) different indicators of a shift across the food web: multimodality and resilience indicators (standard deviation and autocorrelation), and (3) examined the synchronicity of the detected indicators at multiple-trophic levels. Generalized additive models fitted to the ordination scores of the assemblages analyzed revealed two transitions: ca. 1860–1900, and 1915–1990. Ecological indicators of regime shifts revealed that the first transition is consistent with a threshold state response (change in the ecosystem state manifest as a jump when the driver exceeds a state threshold), and the second one with a critical transition (hysteretic transition in which the system change to an alternate stable state). After the first transition lake structure shifted from littoral to pelagic species dominance (evidenced by Cladocera and diatom assemblages), and turbidity increased, indicating a rise in lake water level. This transition was non-linear, showed multimodality, and is most likely driven by an increase in precipitation registered in the region since 1870. During the second transition, nutrient levels rose, all indicators showed multimodality, non-linear dynamics and an increase in standard deviation prior to the regime shift. These dynamics are consistent with a critical transition in response to eutrophication, and coincides with a post-1920 change in land use. Our results show that several ecological indicators of regime shifts need to be examined to perform an accurate diagnosis. We highlight the relevance of a multi-proxy approach including multiple-trophic level responses as the appropriate scale of analysis to determine the occurrence, type and dynamics of regime shifts. We also show that resilience indicators and critical transitions can be detectable in the whole food web and that shallow lakes can undergo different types of regime shifts.Fil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Musazzi, Simona. Consiglio Nazionale delle Ricerche; ItaliaFil: Cordoba, Francisco Elizalde. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Salta. Instituto de Ecorregiones Andinas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Mendiolar, Manuela. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Lami, Andrea. Consiglio Nazionale delle Ricerche; Itali
Phoneme and Sub-Phoneme T-Normalization for Text-Dependent Speaker Recognition
Test normalization (T-Norm) is a score normalization technique that is regularly and successfully applied in the context of text-independent speaker recognition. It is less frequently applied, however, to text-dependent or textprompted speaker recognition, mainly because its improvement in this context is more modest. In this paper we present a novel way to improve the performance of T-Norm for text-dependent systems. It consists in applying score TNormalization at the phoneme or sub-phoneme level instead of at the sentence level. Experiments on the YOHO corpus show that, while using standard sentence-level T-Norm does not improve equal error rate (EER), phoneme and sub-phoneme level T-Norm produce a relative EER reduction of 18.9% and 20.1% respectively on a state-of-the-art HMM based textdependent speaker recognition system. Results are even better for working points with low false acceptance rates
Changes in planktivory and herbivory regimes in a shallow South American lake (Lake Blanca Chica, Argentina) over the last 250 years
Shallow lakes are vulnerable ecosystems impacted by human activities and climate change. The Cladocera occupy a central role in food webs and are an excellent paleoecological indicator of food web structure and trophic status. We conducted a paleolimnological study in Lake Blanca Chica (Argentina) to detect changes on the planktivory and herbivory regimes over the last 250 years. Generalized additive models were fitted to the time series of fish predation indicators (ephippial abundance and size, mucrone size, fish scales, and the planktivory index) and pheophorbide a concentration. The cladoceran assemblage changed from littoral-benthic to pelagic species dominance and zooplankton switched from large-bodied (Daphnia) to small-bodied grazers (Bosmina) ca. 1900 due to increased predation. The shift in planktivory regime (ca. 1920-1930), indicated by fish scales and the planktivory index, as well as herbivory (ca. 1920-1950), was triggered by eutrophication. Changes in planktivory affected the size structure of Bosmina, reducing its body size. This study describes the baseline for the lake as well as the profound changes in the composition and size structure of the zooplankton community due to increased predation and the shift in the planktivory regime. These findings will provide a reference status for future management strategies of this ecosystem.Fil: Carrozzo, David Ricardo. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de BiologĂa; ArgentinaFil: Musazzi, Simona. Consiglio Nazionale delle Ricerche; Italia. Water Research Institute; ItaliaFil: Lami, Andrea. Consiglio Nazionale delle Ricerche; Italia. Water Research Institute; ItaliaFil: Cordoba, Francisco Elizalde. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Salta. Instituto de Ecorregiones Andinas; ArgentinaFil: Gonzalez Sagrario, Maria de Los Angeles. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin
Gravity assisted dark energy dominance and cosmic acceleration
It is proposed that dark energy may become dominant over standard matter due
to universe expansion (curvature decrease). Two models: non-linear
gravity-matter system and modified gravity may provide the effective phantom or
effective quintessence dark energy which complies with the conjecture. It is
interesting that future of such universe is not necessary finite time
singularity (Big Rip). The effective quintessence naturally describes current
cosmic speed-up.Comment: RevTeX4, 4 pages, minor changes, version to appear in PL
Is the future universe singular: Dark Matter versus modified gravity?
The fundamental problem of the occurrence/removal of finite-time future
singularity in the universe evolution for coupled dark energy (DE) is
addressed. It is demonstrated the existence of the (instable or local minimum)
de Sitter space solution which may cure the Type II or Type IV future
singularity for DE coupled with DM as the result of tuning the initial
conditions. In case of phantom DE, the corresponding coupling may help to
resolve the coincidence problem but not the Big Rip (Type I) singularity issue.
We show that modified gravity of special form or inhomogeneous DE fluid may
offer the universal scenario to cure the Type I,II,III or IV future singularity
of coupled (fluid or scalar) DE evolution.Comment: LaTeX 9 page
Effect of Ion Bombardment on the Chemical Properties of Crystalline Tantalum Pentoxide Films
The effect of argon ion bombardment on the chemical properties of crystalline
TaO films grown on Si(100) substrates by radio frequency magnetron
sputtering was investigated by X-ray photoelectron spectroscopy. All samples
were irradiated for several time intervals [(0.5, 3, 6, 9) min] and the Ta
and O core levels were measured each time. Upon analysis at the surface of
the films, we observe the Ta spectrum characteristic of TaO.
Irradiated samples exhibit the formation of Ta suboxides with oxidation states
Ta, Ta, Ta, Ta, and Ta. Exposing the films,
after ion bombardment, to ambient for some days stimulates the amorphous phase
of TaO at the surface suggesting that the suboxides of Ta are unstable.
Using a sputtering simulation we discuss that these suboxides are largely
generated during ion bombardment that greatly reduces the oxygen to tantalum
ratio as the irradiation time increases. The computer simulation indicates that
this is due to the high sputtering yield of oxygen.Comment: 12 pages, 8 figure
Unifying phantom inflation with late-time acceleration: scalar phantom-non-phantom transition model and generalized holographic dark energy
The unifying approach to early-time and late-time universe based on phantom
cosmology is proposed. We consider gravity-scalar system which contains usual
potential and scalar coupling function in front of kinetic term. As a result,
the possibility of phantom-non-phantom transition appears in such a way that
universe could have effectively phantom equation of state at early time as well
as at late time. In fact, the oscillating universe may have several phantom and
non-phantom phases. As a second model we suggest generalized holographic dark
energy where infrared cutoff is identified with combination of FRW parameters:
Hubble constant, particle and future horizons, cosmological constant and
universe life-time (if finite). Depending on the specific choice of the model
the number of interesting effects occur: the possibility to solve the
coincidence problem, crossing of phantom divide and unification of early-time
inflationary and late-time accelerating phantom universe. The bound for
holographic entropy which decreases in phantom era is also discussed.Comment: 13 pages, clarifications/refs added, to match with published versio
Universal procedure to cure future singularities of dark energy models
A systematic search for different viable models of the dark energy universe,
all of which give rise to finite-time, future singularities, is undertaken,
with the purpose to try to find a solution to this common problem. After some
work, a universal procedure to cure all future singularities is developed and
carefully tested with the help of explicit examples corresponding to each one
of the four different types of possible singularities, as classified in the
literature. The cases of a fluid with an equation of state which depends on
some parameter, of modified gravity non-minimally coupled to a matter
Lagrangian, of non-local gravity, and of isotropic turbulence in a dark fluid
universe theory are investigated in detail
Influence of post-deposition annealing on the chemical states of crystalline tantalum pentoxide films
We investigate the effect of post-deposition annealing (for temperatures from
848 K to 1273 K) on the chemical properties of crystalline TaO films
grown on Si(100) substrates by radio frequency magnetron sputtering. The atomic
arrangement, as determined by X-ray diffraction, is predominately hexagonal
(-TaO) for the films exposed to heat treatments at 948 K and
1048 K; orthorhombic (-TaO) for samples annealed at 1148 K and
1273 K; and amorphous for samples annealed at temperatures below 948 K. X-ray
photoelectron spectroscopy for Ta and O core-levels were performed to
evaluate the chemical properties of all films as a function of annealing
temperature. Upon analysis, it is observed the Ta spectrum characteristic
of Ta in Ta and the formation of Ta-oxide phases with oxidation states
Ta, Ta, Ta, and Ta. The study reveals that the
increase in annealing temperature increases the percentage of the state
Ta and the reduction of the others indicating that higher temperatures
are more desirable to produce TaO, however, there seems to be an
optimal annealing temperature that maximizes the O\% to Ta\% ratio. We found
that at 1273 K the ratio slightly reduces suggesting oxygen depletion.Comment: 7 pages, 1 table, 6 figures. arXiv admin note: text overlap with
arXiv:1804.02067, arXiv:1704.0551
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